1. Field of the Invention
The present invention generally relates to a current generator, and more particularly, to a current generator having a high efficiency and a high current matching.
2. Description of Related Art
FIG. 1A is a circuit diagram illustrating a conventional current mirror. Current mirror technology is a widely used method for providing a stable current. With respect to a conventional current mirror as shown in FIG. 1, a current of each channel is obtained by mirroring from a reference current IREF1 via a transistor Tr1. Lower voltage drops between drain-sources of transistors Tr2, Tr3 . . . are helpful for improving an efficiency of the current mirror in its entirety. However, in such a conventional current mirror, in order to decrease errors of the currents i1, i2 . . . of the channels and improve the matching between the currents i1, i2 . . . of the channels, the transistors Tr2, Tr3 . . . of the current mirror cannot be designed for operating in a linear region and the transistors Tr2, Tr3 must be implemented with long channel transistors. Unfortunately, this causes great voltage drops between the drain-sources of the transistors Tr2, Tr3 . . . , thus decreasing the efficiency of the current mirror in its entirety.
FIG. 1B is a circuit diagram illustrating a current mirror further employing an operational amplifier. In order to improve the efficiency of the current mirror in its entirety, conventionally, operational amplifiers 101 are often employed for coupling with gates of the transistors Tr2, Tr3 . . . of the current mirror, for introducing an operational amplifier 101 feedback mechanism. The operational amplifiers 101 are provided for controlling the transistors Tr2, Tr3 . . . to operate in the linear region. The resistors R with small resistance are further employed for reducing additional voltage drops. In such the way, voltage drops between the drain-sources can be reduced, and the entire efficiency of the current mirror can be improved. However, different offset voltages of operational amplifiers 101 of different channels often cause errors of currents i1, i2 . . . of the channels. This decreases the matching of the currents.